The present invention relates to a lip type seal which seals a circumference of a rotary shaft of various sorts of equipments.
FIG. 2 shows such a conventional lip type seal. In FIG. 2, a case 101 is tightly fitted and fixed to an inner circumferential surface of a housing 1 of the lip type seal through a gasket part 102a. A lip member 102 made of elastomer, a resin lip member 103 on the rear side of the lip member 102 and a second resin lip member 104 on the rear side thereof are held to the case 101. When a sealed space S becomes high in pressure, leakage of a fluid as the seal object is prevented. When the sealed space S becomes vacuum state, the vacuum state is held.
In a lip type seal 100 shown in FIG. 2, the lip member 102 on the closest side to the sealed space S is limited by a pressure durable reinforcing ring 105 arranged on the rear surface thereof in deformation due to pressure of the sealed space S. A spiral groove 102b producing pumping function in the leakage direction from the sealed space S by the rotation of the rotary shaft 2 is formed on an inner circumference sliding surface.
The resin lip member 103 disposed on the rear side of the lip member 102 made of elastomer is restricted in deformation in an axial direction by a diameter direction part 103a in the outer circumference being grasped between the pressure durable reinforcing ring 105 on the front side and the rear surface support plate 106 on the rear side. A spiral groove 103b producing a pumping function in the reverse direction to the leakage by the rotation of the rotary shaft 2 is formed on the inner circumference sliding surface.
The second resin lip member 104 arranged on the rear side of the resin lip member 103 is held in the state separated from the resin lip member 103 through an outer circumference spacer part 106a of the rear surface support plate 106 and a front surface support plate 107 disposed to abut on the rear end surface of the outer circumference spacer part 106a. The diameter direction part 104a is grasped between a second rear surface support plate 108 on the rear side of the diameter direction part 104a and the front surface support plate 107. Thereby, deformation in an axial direction is restricted. Also, when the lip type seal 100 is incorporated into the outer circumference of the rotary shaft 2, the front surface support plate 107 serves as a guide in which the second lip member 104 is bent at the inner circumference side.
According to the aforementioned conventional lip type seal, the rear surface of the second rear surface support plate 108 abuts on the end surface of the housing 1. Therefore, the second rear surface support plate 108 is not deformed to the side of the atmosphere A. However, in the rear surface support plate 106, only the outer circumferential part is constrained through the outer circumference space part 106a. Therefore, if high pressure acts on the front surface of the resin lip member 103, the rear surface support plate 106 is subjected to large load in an axial direction through the diameter direction part 103a of the resin lip member 103. As a result, the moment of the inner diameter side becomes large, and as shown in broken line in FIG. 2, the rear surface support plate 106 is greatly deformed in bending to the side of the atmosphere A.
Also, the inner diameter of the rear surface plate 106 and that of the second rear surface support plate 108 are formed into the minimum diameter considering the deviation of the rotary shaft 2 in a diameter direction and the maximum amount of the mounting eccentricity, in order that not entering of the resin lip member 103 into the gap G between the outer circumferential surface of the rotary shaft 2 and the rear surface plates 106, 108. Therefore, it is preferable that the gap G is made as small as possible. However, the inner diameter edge part 106b of the rear surface support plate 106 formed to bend to the side of the sealed space S, corresponding to the bending part of the resin lip member 103, is slightly displaced to the inner diameter side due to the aforementioned deformation to the side of the atmosphere A. Therefore, if the gap G is made small, the inner diameter edge part 106b may come into contact with the outer circumferential surface of the rotary shaft 2 being rotated. On account of such contact, abnormal sound may be produced or large torque may act on a gasket part 102a to produce slippage. Hence the lip type seal 100 may be broken.
An object of the present invention is to provide a lip type seal which prevents bending deformation of a rear surface support plate due to pressure of a sealed space and is excellent in pressure durability.
In a lip type seal according to one embodiment of the present invention, a case is tightly fitted and fixed to an inner circumferential surface of a housing through gasket means. A resin lip member constituted by an inner circumference seal part extending in a bent state from a diameter direction part and its inner circumference to a sealed space side and forming a seal surface between an outer circumferential surface of a rotary shaft and the resin lip member, a rear surface support plate disposed to abut on a rear surface of the diameter direction part of the resin lip member, and a stopper with a rear surface supported to the rising surface side of the housing and the top end coming close to or coming into contact with a rear surface of the inner circumferential part of the rear surface support plate, are provided on the inner circumference of the case.
In addition, xe2x80x9cfront surfacexe2x80x9d in the present specification means a surface facing the sealed space side, xe2x80x9crear surfacexe2x80x9d means a surface facing the opposite side of the sealed space, xe2x80x9cfront sidexe2x80x9d means the sealed space side, and xe2x80x9crear sidexe2x80x9d or xe2x80x9cback sidexe2x80x9d means the opposite side of the sealed space.